Fix thread-safety crash and multipart upload deadlock#39
Merged
patricioxavier8 merged 1 commit intoApr 30, 2026
Merged
Conversation
- Add NSLock to progressHandlersByTaskID dictionary to prevent data race crashes under concurrent access - Clean up progress handlers on upload completion to fix memory leak - Replace waitUntilAllOperationsAreFinished() with async-safe withCheckedContinuation to prevent cooperative thread pool exhaustion during multipart uploads
sg-gs
approved these changes
Apr 30, 2026
patricioxavier8
deleted the
fix/upload-thread-safety-and-multipart-deadlock
branch
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
2 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Problem
Two issues discovered under high-concurrency backup workloads:
EXC_BAD_ACCESS in Upload.uploadEncryptedFile — The progressHandlersByTaskID dictionary is accessed from multiple threads without synchronization. When 10 uploads write to it simultaneously, the dictionary's internal buffer can be reallocated mid-access, causing a segfault.
Multipart upload deadlock in NetworkFacade.runMultipartUpload — waitUntilAllOperationsAreFinished() is a blocking call that holds the current OS thread indefinitely. When multiple large files (>100MB) trigger multipart uploads concurrently, all threads in Swift's cooperative thread pool get blocked, leaving no threads available to execute the actual upload part operations → deadlock.
Solution
Made progressHandlersByTaskID thread-safe using NSLock and added cleanup on completion to prevent memory leaks.
Avoided retain cycles by using [weak self] and a taskRef pattern.
Replaced a blocking operationQueue.waitUntilAllOperationsAreFinished() with an async-safe alternative using withCheckedContinuation, preventing thread pool exhaustion.